Solvent-controlled synthesis of three-dimensional TiO2 nanostructures via a one-step solvothermal route

Three-dimensional (3D) TiO2 nanostructures with various microstructures have been successfully synthesized by altering the solvent via a surfactant-free and single-step solvothermal route. The effects of the solvent on the microstructures of 3D TiO2 nanostructures were investigated. 3D dandelion-like TiO2 structures self-assembled of nanorods were synthesized in non-polar solvent based on water-non-polar solvent interface. For the product derived from the solvent of n-hexane, the 3D microspheres have a homogeneous size distribution in diameter of about 2 mu m and a uniform morphology of radially packed nanorods of 15 nm in diameter along a [001] preference growth direction. A three-step growth model is proposed to illustrate the growth mechanism of TiO2 nanorods self-assembled into 3D dandelion-like structures. Microspheres composed of nanoparticles are obtained using low polar or polar solvent such as n-butyl alcohol and ethanol, which are also amphiphilic solvents. The amphiphile bilayer capped outside the particle serves as the microreactor and soft temple for crystal growth. Only bulky aggregated TiO2 nanoparticles were obtained when pure water is used as the solvent due to the fast hydrolysis of titanium precursor. Mechanisms of the self-assembly of 3D TiO2 structures in different solvents were proposed.